1. Field of the Invention
The present invention relates to a photodetector module for optical communication incorporating a front-end circuit used as a photodetector for an ultra-high speed light transmitting system and a photodetector unit.
2. Related Background Art
A photodetector module for optical communication which photoelectrically converts a high-speed signal with a signal speed on the order of Gbits/s or more is required to minimize the parasitic impedances between elements to attain high-speed characteristics. A front-end circuit using bump bonding (flip chip bonding) can be effectively used for this purpose.
The technique disclosed in Japanese Patent Laid-Open No. 2-297511 is known, in particular, as a photodetector module for optical communication incorporating such a front-end circuit. FIG. 6 is a sectional view showing the arrangement of this photodetector module for optical communication.
As shown in FIG. 6, a front-end circuit 51 is constituted by a photodiode 52 and an electronic circuit element 53 which are connected by bump bonding. The front-end circuit 51 is connected to a circuit board 54 through solder bumps 56 by bump bonding such that the photodiode (PD) 52 is inserted in a hole 55 in the circuit board 54. An optical fiber 57 is fixed with a fiber support part 58. An optical signal output from the optical fiber 57 is focused on the photodiode 52 through a spherical lens 59 and the hole 55. An electrical signal output from the photodiode 52 is output to the outside through the electronic circuit element 53, the solder bumps 56, the interconnections on the circuit board 54, and a high-frequency pin 60. The circuit board 54, the spherical lens 59, and the fiber support part 58 are supported on a base/optical coupling part holder 61.
This arrangement is characterized in that the front-end circuit 51 to which the photodiode 52 is connected by bump bonding is further connected to the circuit board 54 by bump bonding. Bump bonding can greatly reduce the parasitic impedance accompanying the above two connections as compared with wire bonding and other conventional bonding methods. Ultra-high-speed operation of about 10 Gbits/s can be realized.